Winglets have been known for years and have been mounted on aircraft such as, for example, the LEAR JET 28 or American KC 135. It is known that such winglets comprise substantially vertical walls placed on the wing tips of an aircraft which have the property of straightening out the swirling air currents at the wing tip. Actually, in flight, excessive air pressures are produced on the under surface of the wing and, on the other hand, low pressures act on the upper wing surface. The air at the tip of the wings therefore tends to move from the under wing surface to the upper wing surface and thus create vortices at the wing tip. Winglets make it possible to modify the lift distribution all along the wing span and thus improve the aerodynamic efficiency of the wing.
The considerable stresses to which the aircraft structures are subjected are not continuous but occasional. For example, while the aircraft cruises at altitude, the wing often supports only a load corresponding approximately to the weight of the aircraft. However, in the occasional instances of a sharp turn or in a turbulent atmosphere the wing must support a load equal to several times the weight of the aircraft (between 4 and 15 times, depending on the type of aircraft). U.S. Pat. Nos. 4,190,219; 4,205,810 and 4,245,804 disclose very specific forms relating to particular winglets fastened onto the wing tips which although improving the aerodynamics of the wing, also unfortunately cause a constant increase in the stresses on the wings, particularly in the occasional extreme cases discussed above. These extreme stresses, although in actuality occurring only occasionally, must be taken into account in designing the resistant structure of the aircraft, and the mass of this structure which is thereby increased. Thus, what is gained, on the one hand, in aerodynamics, is lost in great part in the form of added structural mass.
Further, in the prior art, there are fins placed at the end of the wings on aircraft having a pronounced sweepback so that their position well aft on the aircraft gives them a stabilizing role like a standard aircraft fin. When these fins are mobile or comprise a mobile rudder, the two surfaces thus created are not always symmetrical in relation to the aircraft plane of symmetry in order to create a moment enabling the aircraft to turn around its yaw axis (recalling that the yaw axis is generally vertical when the aircraft is horizontal). Actually, these fins do not at all have the same function as winglets which do not have a considerable role or effect on the stability of the aircraft.